#10 Homogeneity in API naming

[Reylak]

It is suggested by Lolman to:

• use something like Image() to create a new Image, Sprite() for a new Sprite, etc.
• give for all destructors the same name (would be destroy() then)
• screen should have a capital letter just like all the other classes
• some getters doesn't have 'get' in their names
• another name for dsUser (maybe User can be good finally...)